This invention relates to a frictional power transmission chain for a pulley-type power transmission device, and in particular to such a chain for a stepless transmission or the like.
It is well known in the art that a rubber V-belt can be used as a power transmission element between shafts having pulleys and that a V-belt can be used in a stepless transmission having a split pulley with movable slanting faces. A metallic V-belt having a steel band in a rubber V-block has also been developed in recent years (See Japanese Laid-Open Appln. No. 54-52253).
It is also known that certain disadvantages of the steel band used in this metallic V-belt can be eliminated as disclosed in Japanese Laid-Open Appln. No. 59-17043. In the device disclosed in Appln. No. 59-17043, a link chain is utilized in place of a steel band. Fatigue of a steel band results from tension along the outer side of bends in the band and corresponding compression on the inner side of bands in the band when the band is bent in passing around the driving and driven pulleys. By using chain link, bending stress on a belt is eliminated. However, in the aforesaid Appln. No. 54-52253, the connected links and the V-block in which the link chain is carried still permit sliding relative to one other. In this respect the chain links and the former steel band are similarly stressed and achieve similar results.
Both the steel band and chain link known devices have a common constitution in that the underlying steel bands or chains are assembled with the resilient V-block in a way that enables relative sliding between the V-block and the chain or band due to compression and tension applied to the band in bending around pulleys.
In such a case of sliding movement occurring between parts of an outer V-block and an inner steel band or link chain when the belt is bent when passing around the pulleys, the V-block and steel band or link chain will wear due to this repeating movement occurring on every circuit of the belt. As a result, the durability of the metallic V-belt is inordinately decreased.
Structures of this type are based on a technical concept in which substantial power is transmitted through thrust forces between the individual incremental sections of the belt. The steel band and the link chain are not needed for direct transmission of this power and instead function to keep the successive V-blocks in an endless band form where, upon rounding the pulley, successive belt sections will effectively push the next-leading sections forward from the pulleys as the belt straightens. As a result of the endless band form, relative movement between V-block and steel band or link chain is necessarily produced. Sliding occurs in these devices when the band is forced repeatedly and momentarily to bend into a radius around each pulley.
Furthermore, the steel band or the link chain of the prior art is so much less resilient than the V-block that under tension and compression forces, that a balanced condition as needed in view of the pressing force of the V-groove of the V-pulley is defined by the steel band or chain. The material of the V-block is resiliently forced to comply, so that the varying tension force directly causes fatigue, wear and eventual loss of the band and the chain.